For a number of years, ball propelling machines have been used as a training aid in a variety of sports. Whilst there are a number of different types of ball machines presently available, machines employing expanding gas, such as compressed air, to propel the ball from the machine offer distinct advantages over other types that use counter-rotating wheels or a mechanical arm. In particular, machines employing expanded gas can more easily be adapted to accurately apply spin to a ball prior to firing. Thereby, these machines are better able to simulate balls thrown in actual games, such as the curveball or fastball thrown by pitchers in baseball.
An example of a ball machine which uses expanding gas is described in co-pending International Application No. PCT/AU2003/001188, which is an earlier application of the present inventors. This application describes a pitching machine which uses expanding gas to propel a ball down a barrel towards a target. A predetermined amount of spin can be applied to the ball prior to firing so as to simulate different types of pitches. PCT/AU2003/001188 is hereby incorporated in its entirety by cross-reference. AU 2004904357 is another application of the present inventors that discloses a ball machine which uses expanding gas. AU 2004904357 is also incorporated in its entirety by cross-reference.
At least in theory, the velocity of a ball fired from an expanding gas powered ball machine is proportional to the pressure of the compressed gas used to prime the machine. Accordingly, adjusting the pressure of the compressed gas used should predetermine the velocity of a ball fired from the machine. However, to date, there have been difficulties in manufacturing a machine that can accurately and repeatedly propel a seamed ball at a desired velocity, even where identical gas pressure has been employed.
Accordingly, there exists a need in the art for an expanding gas powered ball machine that offers advantages in terms of accurately and repeatedly imparting a predetermined velocity to a seamed ball propelled therefrom.